I learned to do the same thing, but I use the wash-a-way that is sticky on one side. That way it stays in place and I don't have to fool around with getting everything lined up to go in the serger.
You can use the same idea on your regular sewing machine also, when the fabric is to thin or skips stitches on a knit.
Smart idea. Hopefully I will remember when I have the same issue. Thanks for sharing.